This invention relates to collapsible structures of the types disclosed in U.S. Pat. Nos. 3,968,808 and 4,026,313. In such structures, a network of column-like elements are pivotally joined together for movement between a collapsed, compact disposition and an opened condition in which the desired structural shape is formed. The shape may take many forms and may even be an essentially flat structure suitable for use as a panel or the like.
In any event, the column-like elements are arranged in groups having common ends pivotally together as, for example, by the hub assembly illustrated in FIGS. 12-14 of U.S. Pat. 3,968,808 or in FIGS. 13-16 of U.S. Pat. No. 4,026,313. Because of the complex nature of the network of column-like elements and the necessity for pivotally joining the ends of such elements, the hub assemblies must allow not only the basic pivotal motion, but they must also accommodate more complex relative movements among the column-like elements, specifically, for twisting and/or flexing at the hubs. Additionally, for practical and economical reasons, the column-like elements must be readily assembled with the hub structures while, at the same time, each hub assembly must be capable of withstanding many cycles of opening and collapsing the structure without creating or imposing excessive stress and strain on the column-like elements and, in particular on the pivotal connections between these elements proper. Stated otherwise, the hub assemblies must accommodate for twisting and flexure thereat incidental to opening and collapsing movement but they must also impart sufficient ruggedness and strength as to hold the network of elements accurately and rigidly in the opened condition.